Build A depends on build B (or in fact on artifacts published by build B), and while build B was successful, build A failed. The failure is caused by changes in the sources checked out by build B and handed over in some shape to build A via the published artifacts. As a result, the actual culprit was not notified, since the failure-causing sources were not checked out by build A, but only in build B; and the notification was obviously sent from build A.
Add a flag (most probably in either the repository specification of build B, or in the repository's corresponding checkout step of build B?) that optionally allows to propagate changes to dependent builds -- so that the actual culprit is notified (too).